In recent years, a transcranial magnetic stimulation treatment is increasingly receiving attentions as a treatment method to patients of various neural diseases for which medication is not always effective. The transcranial magnetic stimulation treatment is a relatively new treatment method for applying magnetic stimulation to a particular region of the brain (brain nerve, for example) by a magnetic field generating source provided on the surface of a patient's scalp, thereby capable of providing a treatment and/or relieving symptoms. Unlike the conventional electric stimulation requiring a craniotomy procedure and using an implanted electrode that makes a patient highly uncomfortable, the transcranial magnetic stimulation treatment is expected to be broadly used as a treatment method that is non-invasive and less stressful for patients.
As a specific method of such a transcranial magnetic stimulation treatment, there is known a method of applying electrical current to a coil positioned near the surface of a patient's scalp, regionally generating a small pulsed magnetic field, generating eddy current within a cranium based on a principle of electromagnetic induction, and applying stimulation to the brain nerve immediately under the coil (see Patent Literature 1, for example).
According to Patent Literature 1, it is confirmed that the transcranial magnetic stimulation treatment provided according to the above method effectively relieves intractable neuropathic pains, and in addition, provides a higher effect for pain relief by applying focal stimulation more accurately. However, it is also disclosed that optimum stimulating portions of individual patients are delicately different.
Therefore, in order to achieve a higher effect with the transcranial magnetic stimulation treatment, it is important how an optimum stimulating portion on a patient's head is determined for each patient, or more specifically, how three-dimensional positioning of a treatment coil to the patient's head is performed accurately. It should be noted that it is also known that even if the position of the treatment coil is the same, an achieved effect varies depending on an orientation (posture) of the coil.
Known configurations of the positioning of such a treatment coil include positioning of a treatment coil on the patient's head utilizing an optical tracking system using infrared rays (see Patent Literatures 2 and 3, for example), and some are commercially available and applied in clinical settings.
As described above, in order to achieve an effect for pain relief with the transcranial magnetic stimulation treatment, it is necessary to specify an optimum stimulating portion on a patient's head and accurately apply stimulation to the brain nerve at the portion. While it is difficult to grasp an accurate position of the brain within the cranium from outside, it is possible to grasp its position accurately using three-dimensional information of an MRI (Magnetic Resonance Imaging) image of the head. By using a positioning function of the optical tracking system while referring to the three-dimensional information within the cranium obtained based on the MRI image, a practitioner (such as a doctor) of the transcranial magnetic stimulation treatment is able to guide the treatment coil to the optimum stimulating portion on the patient's head and to apply magnetic stimulation accurately.
Conventionally, when using the optical tracking system in the transcranial magnetic stimulation treatment in such a manner, an infrared reflection marker is provided for each of a static position associated with the patient's head (e.g., a bed in which the patient lies) and the treatment coil, and a current position of the treatment coil is estimated based on a positional relation between these two obtained by detecting the markers, and the treatment coil is guided to the optimum stimulating portion on the patient's head while referring to the three-dimensional information within the cranium obtained based on the MRI image. Therefore, accurate positional alignment between the patient's head and the MRI image is required. Accordingly, accurate positional alignment with the MRI image is performed by specifying the eye, the ear, the nose, or the like using a calibration marker in a state in which the patient's head is fixed to the bed.